Incessantly exposed to temperature of hot corroding gases as well as the impact and abrasive wear caused by the charge, the refractory linings of blast furnaces are likely to spall, collapse or fall off. In addition to shortening the furnace life, such defective linings also impair the operating performance of the blast furnace as a result of heavy deformations in its vertical and circumferential profiles, especially in the upper and middle parts of the shaft. The misshaped furnace profile causes the reducing gas to rise through the furnace is an uneven pattern, thus creating undesirable turbulences. At the same time, coke and sinter get mixed with each other more readily, bringing about an increase in the coke and other fuel consumption and a drop in productivity through the uneven reducing of the charge.
As a solution for such problems, an attempt has been made to inject monolithic refractories through an opening made in the steel shell and furnace wall covering the damaged portion. But it has turned out that the monolithic refractories thus applied do not have the desired durability since they come off easily, lacking adequate adhesiveness, when hit by the descending charge. This method has thus proved unfit for use in the repairing of the shaft of the blast furnace. In addition, this method requires a long repairing time.